The present invention relates to a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages.
It is known to form exhaust passages and a converging area into which the exhaust passages converge internally in a cylinder head as shown in Japanese patent No. 2709815. Japanese UM publication No. 5-44499 discloses engines in which an oxygen sensor for detecting an oxygen concentration is placed in an exhaust manifold and in an exhaust pipe downstream to the exhaust manifold.
As an oxygen sensor is incapable of operating while the engine is still cold, it is preferable to mount the oxygen sensor as close to a combustion chamber as possible. However, if it is provided upstream of the exhaust manifold, it is exposed only to the exhaust gas produced from one of the cylinders, and incapable of giving the oxygen concentration of the overall exhaust gas. It is conceivable to provide an oxygen sensor for each combustion chamber, but it increases the cost and weight of the engine.
In view of such problems of the prior art, a primary object of the present invention is to provide a multi cylinder internal combustion engine having a compact exhaust manifold arrangement internally defined in a cylinder head.
A second object of the present invention is to provide a multi cylinder internal combustion engine which allows an oxygen sensor to be mounted relatively close to the combustion chamber while permitting the sensor to be uniformly exposed to the exhaust gas from the combustion chambers of an entire cylinder bank.
A third object of the present invention is to provide a multi cylinder internal combustion engine which can activate an oxygen sensor with a minimum warm up time period.
A fourth object of the present invention is to provide a multi cylinder internal combustion engine which can protect an oxygen sensor from an excessive temperature rise.
A fifth object of the present invention is to provide a multi cylinder internal combustion engine which provides a favorable mounting position for an oxygen sensor while providing a favorable cylinder head arrangement.
A sixth object of the present invention is to provide a multi cylinder internal combustion engine which provides a favorable mounting position for an oxygen sensor so as to prevent damages to the oxygen sensor by being hit by an external object.
According to the present invention, these and other objects can be accomplished by providing a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages extending from a plurality of combustion chambers defined in part by the cylinder head, the exhaust passages converging into a converging area also internally defined in the cylinder head, wherein: an oxygen sensor for detecting an oxygen concentration in exhaust gas is passed into the converging area substantially in parallel with a cylinder axial line.
Thus, the oxygen sensor can be mounted relatively close to the combustion chamber while permitting the sensor to be uniformly exposed to the exhaust gas from the combustion chambers of an entire cylinder bank. Therefore, the oxygen sensor can be activated relatively quickly substantially without any warm-up, and can measure the oxygen concentration of the overall exhaust gas. By passing the oxygen sensor in parallel with a cylinder axial line, the sensor is protected from the heat of the converging area. In particular, by passing the sensor downwardly into the converging area from above, the assembly work can be simplified.
In particular, if the converging area and the exhaust passages are defined at least in part by an exhaust passage wall extending laterally from the cylinder head defining an arched profile in a plane perpendicular to a cylinder axial line, and an oxygen sensor for detecting an oxygen concentration in exhaust gas is passed into the converging area, a particularly compact arrangement can be achieved. Also, the mounting position for the oxygen sensor can be gained in a compact manner without requiring any special arrangement.
According to a preferred embodiment of the present invention for a favorable mounting position for the oxygen sensor, an exhaust outlet is defined adjacent to the converging area, and a hole for receiving the oxygen sensor is formed in a part of the cylinder head interposed between a pair of bosses provided adjacent to the exhaust outlet for supporting threaded bolts for joining an exhaust system component to the exhaust outlet.
Once the oxygen sensor has been warmed up to a desired level, it is then desirable to prevent it from an excessively high temperature. To this end, a water jacket may be defined in the cylinder head so as to extend to an adjacent part of the oxygen sensor.
Preferably, the exhaust system component consists of a catalytic converter, and an outer profile of the oxygen sensor is more inwardly located than an outer profile of the catalytic converter. Thus, the damages to the oxygen sensor by being hit by an external object during transportation and assembly work can be avoided. In the case of a V-type engine, preferably, a dimension between outer ends of oxygen sensors for the respective cylinder banks being smaller than a dimension between outer ends of the catalytic converters.